The present invention pertains to medical imaging devices, and more particularly, to ultrasonic imaging catheters used in diagnostic applications.
Presently, minimally invasive imaging devices are employed in the diagnostic analysis of relatively large body cavities, such as, e.g., a heart chamber. Of particular interest to the present invention, ultrasonic imaging catheters have been employed to generate cross-sectional images from within the body cavity. The cross-sectional images reveal the surrounding contour of tissue, secondary structure, and other structural information relevant to treatment and diagnosis of various diseased conditions.
In this connection, a known imaging catheter 20, as depicted in FIG. 1, includes an elongate catheter body 22 with a distally formed elongate acoustic window 24 through which ultrasonic energy transparently passes. The catheter body 22 includes an imaging lumen 26 in which a rotatably and longitudinally translatable imaging core 28 is disposed. The imaging core 28 comprises a drive cable 30 along with a distally connected ultrasonic transducer housing 32 and mounted ultrasonic transducer 34. The transducer 34 is mechanically coupled to a drive unit (not shown) via the drive cable 30 and electrically coupled to a signal processor (not shown) via a transmission line 36 disposed in the drive cable 30. The transmission line 36 may consist of coaxial cable, triaxial cable, twisted pair, or other suitable configurations.
Disposal of the acoustic window 24, at a desired region within the body cavity and subsequent operation of the drive unit and signal processor, generates a longitudinal image scan of the tissue surrounding the body cavity. In particular, the electrical signals are transmitted to and received from the transducer 34, while the transducer 34 is rotationally and longitudinally translated relative to the acoustic window 24. In this manner, a multitude of imaging data xe2x80x9cslicesxe2x80x9d are generated, which can be synthesized to produce a three-dimensional image of the body cavity for analysis by a viewing physician.
The ability to generate a three-dimensional image of a body cavity is advantageous in several respects. First, such an image generally allows a physician to ascertain the existence of a diseased region within the body cavity. Second, if such diseased region is found, the image permits a qualitative assessment of the nature of the disease in order to help select the most effective treatment modality. Third, the image can be used to determine the exact location of the diseased region, or the location of a therapeutic element relative to the diseased region, so that intervention can be directed only at the diseased region and not at healthy regions of the body cavity where the interventional procedure might cause damage.
Referring to FIG. 2, the imaging catheter 20 can be used to generate a three-dimensional image of a region of a heart 50. In particular, the imaging catheter 20 is advanced through the vasculature of the patient until the acoustic window 24 extends into a chamber of the heart 50, such as, e.g., the left ventricle 52. A longitudinal scan of the heart 50 is then performed, thereby generating a multitude of cross-sectional imaging data slices along respective imaging planes, such as, e.g., representative planes P(1)-P(5). Subsequent synthesis of the imaging data slices will result in a single three-dimensional image of heart tissue 50 which is intersected by the imaging planes. Heart tissue 50 not intersected by the imaging planes, such as, e.g., at the apex 54 of the heart 50, will not appear in the three-dimensional image. Thus, the image will not include potentially vital information that could lead to the proper diagnosis and subsequent treatment of a diseased region of the heart 50.
As shown in FIG. 3, the acoustic window 38 can be manipulated inside the heart 50, such that imaging planes of a subsequent longitudinal scan, such as, e.g., representative imaging planes P(6)-P(8), intersect heart tissue 50 not imaged during the first longitudinal scan, such as, e.g., at the apex 54. This task may sometimes be difficult or tedious to perform, and even if apparently successful, may result in a multitude of uncorrelated three-dimensional images, making proper examination of the heart 50 more difficult.
Further, referring back to FIG. 2, the force that the mitral valve 56 and entrance 58 to the left atrium 60 of the heart 50 exerts on the acoustic window 24 may create an arc 38 in the acoustic window 24 through which the heart 50 is imaged. As a result, the imaging data slices which are generated along the imaging planes, such as, e.g., planes P(4) and (P5), may, when synthesized, result in a image which is distorted at the left atrium 60 and right atrium 62, since the relative rotational orientation of the imaging planes P(4) and P(5) are unknown due to the randomness of the geometry of the arc 38.
The present invention overcomes the afore-described drawbacks of a conventional imaging device by providing an imaging device, such as, e.g., an ultrasonic imaging catheter, that includes a pull wire connected to the distal end thereof, such that manipulation of the pull wire forms the distal end of the imaging device into a curvilinear geometry that is known and repeatable.
In a first preferred embodiment, an ultrasonic imaging catheter, according to the present invention, includes an elongate catheter body with a distally formed acoustic window. An imaging core, which includes a drive cable and a distally mounted ultrasonic transducer, is disposed in an imaging lumen of the catheter body. The transducer is disposed in the acoustic window and is rotationally and longitudinally translatable relative thereto. The pull wire is disposed within a pull wire lumen, which may be the same as the imaging lumen, of the catheter body and is connected to the distal tip of the acoustic window. Longitudinal displacement of the pull wire, relative to the catheter body, causes the acoustic window to form into a known and repeatable arc. A stiffening member can be disposed along the acoustic window to provide resilience thereto.
In a preferred imaging method, the acoustic window of the catheter is placed within a cavity of an organ, such as, e.g., the left ventricle of a heart. The acoustic window is formed into an arc, and a curvilinear longitudinal imaging scan is performed through the arc, generating a multitude of cross-sectional imaging data slices respectively along a multitude of imaging planes. Due to the curvature of the acoustic window, the imaging planes have differing relative rotational orientations, which intersect the entire body cavity, thereby providing a single three-dimensional image of virtually the entire body cavity. Since the geometry of the arc is known, any distortion caused by the curvature of the acoustic window can be removed from the three-dimensional image.
In an alternatively preferred imaging method, the imaging catheter is used in conjunction with a therapeutic catheter having a distally located therapeutic element, such as, e.g., an ablation electrode. The acoustic window of the imaging catheter and the ablation electrode of the therapeutic catheter are placed in a body cavity, such as, e.g., the left ventricle of a heart. The imaging catheter is operated, in a similar manner as described above, to obtain a three-dimensional image of the left ventricle. The image generally will include an acoustic artifact caused by the ablation electrode, which can be used to locate the ablation electrode adjacent the diseased region of the left ventricle for subsequent ablation thereof.
In still another alternatively preferred imaging method, the imaging catheter is used in conjunction with another diagnostic catheter and a therapeutic catheter. The diagnostic catheter preferably includes a distal basket structure that includes an array of electrodes. The therapeutic catheter preferably includes a distal therapeutic element, such as, e.g., an ablation electrode. The acoustic window of the imaging catheter, the basket structure of the diagnostic catheter, and the ablation electrode of the therapeutic catheter are maneuvered into a body cavity, such as, e.g., the left ventricle of a heart. The diagnostic catheter is operated to locate the diseased region of the ventricle, with one of the diagnostic electrodes indicating the location thereof. The imaging catheter is operated in a similar manner, as described above, to obtain a three-dimensional image of body organ. The image may include a plurality of acoustic artifacts caused by the diagnostic electrodes and a single acoustic artifact caused by the ablation electrode, which can both be used to locate the ablation electrode adjacent the indicative diagnostic electrode, and thus, the diseased region, for subsequent ablation thereof.
Other and further objects, features, aspects, and advantages of the present invention will become better understood with the following detailed description of the accompanying drawings.